Abstract

Polycyclic aromatic hydrocarbons (PAHs) in mangrove sediment-dwelling biota (crabs and molluscs) from the Calabar River, SE Niger Delta of Nigeria were analyzed using GC-MS in order to assess the degree of contamination of the river by anthropogenic activity. The associated sediment samples (where these biota were collected) showed much higher total PAH (TPAH) concentration (16,028.3 ng/g dry weight (dw)) at the upper mangrove area (UMA) than that found toward the river mouth (MR; 1,667.5 ng/g dw). However, the mean TPAH levels were higher in molluscs (16,749.8 ng/g ww) and crabs (29,325.1 ng/g ww) at theMR, and in molluscs (28,580.8 ng/g ww) and crabs (71,782.6 ng/g ww) at the UMA than in the associated sediments, indicating occurrence of bio-accumulation/bio-concentration of PAHs in tissues of these organisms. The results revealed that molluscs are safer to consume than crabs. One way analysis of variance (ANOVA) indicated no significant relationship between lipid content or body size of organisms and contaminant load probably because of non-equilibrium situation: smaller animals accumulated more PAHs than their larger counterparts, suggesting different uptake and elimination rates for these compounds. Biota-sediment accumulation factors (BSAFs) varied among the organisms (4.84-14.98) and were generally lower for highly polluted site (UMA; fresh water area) and higher for area of low anthropogenic pressure (MR- brackish water area). Risk assessment against USEPA standard show the biota to be highly contaminated with carcinogenic PAHs and may pose life-time cancer risk, especially to residents of the riverine/coastal communities who often consume more of these organisms than those living hinterland.

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